I would say its bad...Is it OK to let a water pump run dry?
I wonder if it's bad to be on when it's lifted out of the reservoir. I also have some design ideas that incorporate a water pump pumping water for a time, then pumping air once the water is pumped out until it shuts off.
Never never never.You'll burn it up.I agree, heat is bad for pumps and with no fluid going through that's what usual happens, heat failure. One exception is mag pumps, the impeller is held in place by a magnetic field not nuts and bolts.
Peace